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Monday, May 3, 2010

The horse-hunting hyenas of Srbsko Chlum-Komin Cave

Breaking down a hyena kill. Given competition with other
carnivores, prehistoric hyenas (like their living counterparts)
would probably have disarticulated and transported parts of
horses they killed. From Diedrich 2010.

In Hollywood films, there is nothing like an assemblage of bones strewn about a cave floor to testify to the power and voraciousness of a predator. Every skeleton is a testament to the hunting prowess of the carnivore, which causes even more alarm when the person who has stumbled into the cave realizes that they have just walked into a literal dead-end.

Although amplified for dramatic effect in the movies, this cinematic convention is based upon fact. Some mammalian carnivores do create bone assemblages in caves, and through the fossil record we know that they have been doing so for millions of years. In fact, the bone-collecting habits of carnivores have proven to be a boon for paleontologists, creating assemblages which not only represent the animals which lived in the area, but also provide clues as to the interactions between predator and prey during the distant past.

One such monument is Srbsko Chlum-Komin Cave in the Czech Republic. Discovered in 1942, this Upper Pleistocene site was once a spotted hyena den, and the activities of these predators caused many of the over 3,500 large mammal bones to become preserved at the site. Over 350 elements from hyena skeletons, bone-filled coprolites (fossil feces), and tooth-marked bones identify the cave as a place where the prehistoric hyenas took parts of their prey in order to consume them in relative peace, but, as explained by paleontologist Cajus Diedrich in Quaternary International, this assemblage is not quite like the other fossil hyena dens found elsewhere in Europe.

Among the other fossil mammals found in Srbsko Chlum-Komin Cave are lions, the woolly rhinocerosCoelodonta antiquitatis, steppe bison, reindeer, and ibex, but the most prevalent mammal by far (represented by approximately 51 percent of the bones) is Przewalski’s horse. Portions of the horse’s skull and limbs are found here in a frequency considerably greater than in other known hyena den sites, and, despite what might be expected for carnivores known to chew and consume bone, relatively few of the horse bones show any sign of being gnawed on.

A comparison of the faunal makeup of Srbsko Chlum-Komin
Cave (left) and Perick Cave (right). Each den site was
located near different habitat types and were home to
different assemblages of large herbivores. From Diedrich 2010

According to Diedrich, the prevalence of horse remains and their generally intact condition may be attributable to two different causes. The first is what kinds of prey were regularly available for the Srbsko Chlum-Komin hyenas. Looking at other hyena-created bone accumulations elsewhere in Europe, horses appeared to make up a larger amount of the hyena diet in places where mammoths, musk ox, and large deer were rare. These differences may simply signal differences in habitat – sites where there are fewer horse remains and more mammoth remains, such as Perick Cave in Germany, are indicative of dens made near flatter grassland habitats which would have been more suitable to mammoths than the rocky habitat around Srbsko Chlum-Komin. Since the Srbsko Chlum-Komin hyenas lived in a place where mammoths and some other large prey were rare, they appear to have gone after horses much more frequently.

And there must have been a lot of horses, Diedrich hypothesizes, because if hyenas are able to frequently acquire meat they consume bone less often. Given the relative infrequency of toothmarked bone in the cave it would appear that the deposit represents a time when the hyenas caught and killed horses so frequently that meat was almost always on the menu. Determining the span of time during which the cave was occupied by hyenas is a difficult task, but it may be that it was inhabited seasonally during a time when there were plenty of horses to catch.

Spotted hyenas giggling over an antelope spine. If a
hyena can rip off and easily carry part of a carcass,
it will often try to take it away from the kill site to
consume it. Courtesy BMC Ecology.

But where are the rest of the horse skeletons? There are plenty of limb bones and skull fragments, but what were the hyenas doing with the rest of the bodies? Just as spotted hyenas often come into competition with other large predators (most prominently lions) for carcasses in Africa today, the cave hyenas of prehistoric Europe also had to contend with lions and other predators. Even if a group of hyenas successfully brought down a horse their kill could be stolen by a pride of lions or even another group of hyenas, and so hyenas developed a habit of dismembering carcasses and carrying off parts to consume away from the squabbling crush of meat-eaters. Since limbs and skulls carry a fair bit of meat and are easy to carry, it is not surprising that they are the best represented horse parts in the cave.

Yet, even now and then, the hyenas probably did manage to drag a mostly-complete horse carcass into their den. Among the new fossils recovered from the Srbsko Chlum-Komin site is a skeleton of a fetal horse, and there is little doubt that it would have still been inside its mother when it died. Why it was never consumed is a mystery, but its presence in the cave appears to indicate that the hyenas dragged the body of a pregnant mare into the cave, ate the choicest bits of the body, and then left the rest.

The skeleton of a fetal horse found inside Srbsko
Chlum-Komin Cave. From Diedrich 2010.

A fossil hyena den is far more than a messy jumble of bones. The identity and position of each skeletal element is just a part of a bigger story which can help paleontologists better understand the interactions of predator and prey during a time when our prehistoric relatives had to contend with the same carnivores and hunted the same prey. Every bone tell a story about the life of an animal, but what happens to a bone after death can tell us even more.

Monday, May 3, 2010

The horse-hunting hyenas of Srbsko Chlum-Komin Cave

Breaking down a hyena kill. Given competition with other
carnivores, prehistoric hyenas (like their living counterparts)
would probably have disarticulated and transported parts of
horses they killed. From Diedrich 2010.

In Hollywood films, there is nothing like an assemblage of bones strewn about a cave floor to testify to the power and voraciousness of a predator. Every skeleton is a testament to the hunting prowess of the carnivore, which causes even more alarm when the person who has stumbled into the cave realizes that they have just walked into a literal dead-end.

Although amplified for dramatic effect in the movies, this cinematic convention is based upon fact. Some mammalian carnivores do create bone assemblages in caves, and through the fossil record we know that they have been doing so for millions of years. In fact, the bone-collecting habits of carnivores have proven to be a boon for paleontologists, creating assemblages which not only represent the animals which lived in the area, but also provide clues as to the interactions between predator and prey during the distant past.

One such monument is Srbsko Chlum-Komin Cave in the Czech Republic. Discovered in 1942, this Upper Pleistocene site was once a spotted hyena den, and the activities of these predators caused many of the over 3,500 large mammal bones to become preserved at the site. Over 350 elements from hyena skeletons, bone-filled coprolites (fossil feces), and tooth-marked bones identify the cave as a place where the prehistoric hyenas took parts of their prey in order to consume them in relative peace, but, as explained by paleontologist Cajus Diedrich in Quaternary International, this assemblage is not quite like the other fossil hyena dens found elsewhere in Europe.

Among the other fossil mammals found in Srbsko Chlum-Komin Cave are lions, the woolly rhinocerosCoelodonta antiquitatis, steppe bison, reindeer, and ibex, but the most prevalent mammal by far (represented by approximately 51 percent of the bones) is Przewalski’s horse. Portions of the horse’s skull and limbs are found here in a frequency considerably greater than in other known hyena den sites, and, despite what might be expected for carnivores known to chew and consume bone, relatively few of the horse bones show any sign of being gnawed on.

A comparison of the faunal makeup of Srbsko Chlum-Komin
Cave (left) and Perick Cave (right). Each den site was
located near different habitat types and were home to
different assemblages of large herbivores. From Diedrich 2010

According to Diedrich, the prevalence of horse remains and their generally intact condition may be attributable to two different causes. The first is what kinds of prey were regularly available for the Srbsko Chlum-Komin hyenas. Looking at other hyena-created bone accumulations elsewhere in Europe, horses appeared to make up a larger amount of the hyena diet in places where mammoths, musk ox, and large deer were rare. These differences may simply signal differences in habitat – sites where there are fewer horse remains and more mammoth remains, such as Perick Cave in Germany, are indicative of dens made near flatter grassland habitats which would have been more suitable to mammoths than the rocky habitat around Srbsko Chlum-Komin. Since the Srbsko Chlum-Komin hyenas lived in a place where mammoths and some other large prey were rare, they appear to have gone after horses much more frequently.

And there must have been a lot of horses, Diedrich hypothesizes, because if hyenas are able to frequently acquire meat they consume bone less often. Given the relative infrequency of toothmarked bone in the cave it would appear that the deposit represents a time when the hyenas caught and killed horses so frequently that meat was almost always on the menu. Determining the span of time during which the cave was occupied by hyenas is a difficult task, but it may be that it was inhabited seasonally during a time when there were plenty of horses to catch.

Spotted hyenas giggling over an antelope spine. If a
hyena can rip off and easily carry part of a carcass,
it will often try to take it away from the kill site to
consume it. Courtesy BMC Ecology.

But where are the rest of the horse skeletons? There are plenty of limb bones and skull fragments, but what were the hyenas doing with the rest of the bodies? Just as spotted hyenas often come into competition with other large predators (most prominently lions) for carcasses in Africa today, the cave hyenas of prehistoric Europe also had to contend with lions and other predators. Even if a group of hyenas successfully brought down a horse their kill could be stolen by a pride of lions or even another group of hyenas, and so hyenas developed a habit of dismembering carcasses and carrying off parts to consume away from the squabbling crush of meat-eaters. Since limbs and skulls carry a fair bit of meat and are easy to carry, it is not surprising that they are the best represented horse parts in the cave.

Yet, even now and then, the hyenas probably did manage to drag a mostly-complete horse carcass into their den. Among the new fossils recovered from the Srbsko Chlum-Komin site is a skeleton of a fetal horse, and there is little doubt that it would have still been inside its mother when it died. Why it was never consumed is a mystery, but its presence in the cave appears to indicate that the hyenas dragged the body of a pregnant mare into the cave, ate the choicest bits of the body, and then left the rest.

The skeleton of a fetal horse found inside Srbsko
Chlum-Komin Cave. From Diedrich 2010.

A fossil hyena den is far more than a messy jumble of bones. The identity and position of each skeletal element is just a part of a bigger story which can help paleontologists better understand the interactions of predator and prey during a time when our prehistoric relatives had to contend with the same carnivores and hunted the same prey. Every bone tell a story about the life of an animal, but what happens to a bone after death can tell us even more.